TY - JOUR

T1 - Orbital Ingredients for Cooking X-structures in Edge-on Galaxies

AU - Parul, Hanna D.

AU - Smirnov, Anton A.

AU - Sotnikova, Natalia Ya

N1 - Publisher Copyright: © 2020. The American Astronomical Society. All rights reserved. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/5/20

Y1 - 2020/5/20

N2 - X-structures are often observed in galaxies hosting the so-called B/PS (boxy/peanuts) bulges and are visible from the edge-on view. They are the most notable features of B/PS bulges and appear as four rays protruding from the disk of the host galaxy and distinguishable against the B/PS bulge background. In some works, their origin is thought to be connected with the so-called banana-shaped orbits with a vertical resonance 2:1. A star in such an orbit performs two oscillations in the vertical direction per one revolution in the bar frame. Several recent studies that analyzed ensembles of orbits arising in different N-body models do not confirm the dominance of the resonant 2:1 orbits in X-structures. In our work, we analyze two N-body models and show how the X-structure in our models is gradually assembled from the center to the periphery from orbits with less than 2:1 frequency ratio. The most number of such orbits is enclosed in a "farfalle"-shape (Italian pasta) form and turns out to be non-periodic. We conclude that the X-structure is akin to the envelope curve of regions of high density caused by the crossing or folding of different types of orbits at their highest points, and does not have a "backbone" similar to that of the in-plane bar. Comparing the orbital structure of two different numerical models, we show that the dominance of one or another family of orbits with a certain ratio of the vertical oscillations frequency to the in-plane frequency depends on the parameters of the underlying galaxy and ultimately determines the morphology of the X-structure and the opening angle of its rays.

AB - X-structures are often observed in galaxies hosting the so-called B/PS (boxy/peanuts) bulges and are visible from the edge-on view. They are the most notable features of B/PS bulges and appear as four rays protruding from the disk of the host galaxy and distinguishable against the B/PS bulge background. In some works, their origin is thought to be connected with the so-called banana-shaped orbits with a vertical resonance 2:1. A star in such an orbit performs two oscillations in the vertical direction per one revolution in the bar frame. Several recent studies that analyzed ensembles of orbits arising in different N-body models do not confirm the dominance of the resonant 2:1 orbits in X-structures. In our work, we analyze two N-body models and show how the X-structure in our models is gradually assembled from the center to the periphery from orbits with less than 2:1 frequency ratio. The most number of such orbits is enclosed in a "farfalle"-shape (Italian pasta) form and turns out to be non-periodic. We conclude that the X-structure is akin to the envelope curve of regions of high density caused by the crossing or folding of different types of orbits at their highest points, and does not have a "backbone" similar to that of the in-plane bar. Comparing the orbital structure of two different numerical models, we show that the dominance of one or another family of orbits with a certain ratio of the vertical oscillations frequency to the in-plane frequency depends on the parameters of the underlying galaxy and ultimately determines the morphology of the X-structure and the opening angle of its rays.

KW - 3-DIMENSIONAL BARS

KW - BOXY-PEANUT

KW - Barred spiral galaxies

KW - DISK

KW - DYNAMICS

KW - Disk galaxies

KW - EVOLUTION

KW - Galaxy bulges

KW - Galaxy dynamics

KW - Galaxy structure

KW - MASS

KW - MODELS

KW - N-body simulations

KW - PHASE-SPACE

KW - SHAPED BULGES

KW - STELLAR

KW - N-body simulations (1083)

KW - Barred spiral galaxies (136)

KW - Disk galaxies (391)

KW - Galaxy dynamics (591)

KW - Galaxy structure (622)

KW - Galaxy bulges (578)

UR - http://www.scopus.com/inward/record.url?scp=85086253258&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/3cc1b0ed-cfdd-3500-aeb8-fdba480e0dca/

U2 - 10.3847/1538-4357/ab76ce

DO - 10.3847/1538-4357/ab76ce

M3 - Article

AN - SCOPUS:85086253258

VL - 895

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 12

ER -